Which Aquaro 6 do you own?
I looked up the only one PPCs sells(Aquaro 6XT... or XLT?) and it's supposedly rated for 30 wpc. I did the math for the Watts per ER 120 and that was 2.16w. No way you're hitting 30w per channel with 10 per channel. Or the configuration you contacted Customer Support with. Not even with an EK fan as they are rated at .18A maximum draw. Ten ER 120s are 21.6w. You should easily be able to fit ten of them on one channel. I'd be extremely surprised if the max capability of any 30wpc controller could only run 30w across the PCB. Especially one that is as well known as the Aquaro. Shoot a Sunbeam Rheosmart 6 can run 30wpc.
I call BS on the support tech that suggests that it's a flaw with EK fans. Maybe that is what the fellow learned, but I believe he's not being honest with you in order to avoid a warranty exchange. It shouldn't matter what fan you put on the device, only its rated Amperage and that you didn't overload the channel with excessive wattage.
And of course if you removed fans against the recommendation of their company. I believe one should ALWAYS shut down their system when installing or removing anything that uses power. I know you don't believe it matters, but what's it hurt if you power the system down and degauss the power from it before doing so? At the very least, you know you won't muff anything by doing so and you won't have any niggling feelings making the hair on the back of your neck stand up.
But 16 total fans across 3 out of 4 channels shouldn't have caused your Aquaro to come up lame. Four .18A rated fans is 8.6w. Six are 12.96w and the same 12.96w for the other channel. No way your D5 is throwing enough current through the 4th channel to overload the spectrum. My D5 isn't handy atm, but I believe that it uses ~10w as an educated rough estimate.
Using your words here, you had ten fans on one channel.
No matter how you slice it, that controller should eaasily be able to absorb 44.6w without an issue. Apparently you likely caught a bad one and didn't realize it until it was too late.
Of course this could all be moot if you have a different Aquaro than the one I looked up and the WPC was less than 20wpc. Cause that's the only way I see that type of degradation occurring over that period of time.